When a power amplifier of a wireless communication device comprises an inverter, it is preferable to make the conduction period (duty ratio) of a pMOS (p-channel) transistor in the inverter and the conduction period (duty ratio) of a nMOS (n-channel) transistor in the inverter the same or substantially so. The reason is being that if the duty ratios are not uniform, symmetry of output signal waveforms output from the power amplifier will be deteriorated and even-order harmonic components in the output signals can be increased. For that reason, the waveform of the output signal needs to be adjusted to a desired waveform by control of the duty ratio(s).